FIG. 9 shows a structure of a prior art DBR surface emitting type laser device, reported in Applied Physics Letters, 50(24), pp 1705 to 1707, 1987 by K. Kojima et al. In FIG. 9, reference numeral 2 denotes a semiconductor substrate. An n side electrode 1 is provided at the bottom of the substrate 2. On the substrate 2, a lower cladding layer 3, an active layer 4, and an upper cladding layer 5 are successively provided. A diffraction grating 7 is provided at the surface of the upper cladding layer 5. A dielectric film 6 is provided on the portion of the upper cladding layer 5 where the distributed Bragg reflector is provided. A contact layer 9 is provided on a current injection region of the upper cladding layer 5. A p side electrode 8 is provided on the surface of the laser. Reference numeral 10a denotes a narrow active region for obtaining a single, fundamental mode oscillation.
The laser operates as follows. The light which transits the resonator is mainly confined in the active layer 4, but a part of the light reaches the upper and lower cladding layers 3 and 5. When diffraction gratings 7 are provided in the upper cladding layer, the advancing direction of light is determined by the phase of the light reflected (scattered) from the respective faces of the diffraction grating. When the interval between the two gratings is an integer multiple of .lambda./2 (where .lambda. is wavelength), the light returns toward the original direction, and the light transits in many directions when the integer multiple is large. When the interval is an even number times of .lambda./2, the light also transits in the direction perpendicular to the substrate 2. This prior art laser device operates as a surface emitting type based on the above-described principle, and the width of the stripe is ordinary narrowed to 3 to 4 microns to obtain a fundamental transverse oscillation mode of the laser.
The prior art DBR surface emitting type semiconductor laser device has a narrow active region stripe, and therefore there arises a problem in that when the injected current is increased to obtain a high output power, destruction of the facet, or Catastrophic Optical Damage (COD) occurs because of heat and the maximum output power is restricted. Furthermore, there arises another problem in that when the active region is widened to obtain a high output power, higher order transverse mode oscillation takes place.